flashback query闪回查询

闪回查询是使用undo数据查询过去某个时间点表中数据，一定程度上可以恢复误操作。主要是DML操作

SQL> select count(*) from hr.tb2;

  COUNT(*)
----------
        19

SQL> select current_scn from v$database;

CURRENT_SCN
-----------
    3187961

SQL> delete from hr.tb2 where rownum<11;

10 rows deleted.

SQL> commit;

Commit complete.

SQL> select count(*) from hr.tb2;

  COUNT(*)
----------
         9

SQL> select count(*) from hr.tb2 as of scn 3187961;

  COUNT(*)
----------
        19

SQL> delete from hr.tb2;

9 rows deleted.

SQL> commit;

Commit complete.

SQL> insert into hr.tb2 select * from hr.tb2 as of scn 3187961;

19 rows created.

SQL> commit;

Commit complete.